Method and apparatus for flash flow processing having feed rate control

Abstract: A material processing apparatus and method for flash flow processing by melt spinning. The invention includes a feed rate controller in combination with a spinner head assembly including a spinner head with a continuous perimeter for providing heat and centrifugal force to a material being processed. The spinner head assembly also includes a spinner drive connected to the spinner head for generating the centrifugal force. The material processing apparatus can also include support for supporting the spinner head assembly, where the feed rate controller is electrically connected to the support. The feed rate controller determines a detected load of material in the spinner head from data provided by the support, compares it to a preselected load for the material being processed and generates a feed rate control signal indicative of a difference between the detected and preselected loads. A feeder assembly supplies the feedstock material to the spinner head at a feed rate defined by the feed control signal.

Description: BACKGROUND OF THE INVENTION The present invention relates to flash flow processing, and, more particularly, to improvements in melt spin processing machines to enhance process capability. Various machines have been designed for spinning feedstock materials, particularly sugar, while at the same time applying heat to the feedstock. The materials may be introduced to a spinner assembly within the spinning machine in molten form or, alternatively, introduced in solid form and heated to the flow point or subjected to flash-flow just prior to being spun out from the spinner assembly. U.S. Patent No. 4,872,821 discloses a spinning machine that is particularly designed for spinning cotton candy. The machine includes a spinner head having slotted, cylindrical walls and heating elements adjacent to each wall. Sugar in solid form is introduced into the spinner head and propelled against the heating elements where it is made flowable and spun out through the slots where it solidifies into the floss-like material known as cotton candy. Various other machines have been designed over the years for spinning cotton candy. One such machine is disclosed in U.S. Patent No. 3,930,043, which corresponds to the preamble of claim 1. This machine includes a helical resistance heating element positioned within a finely perforated shell. The heating element is supported against the inner wall of the shell by spacer elements. As the shell spins, molten sugar moves through the perforations. Similar machines are disclosed in U.S. Patent Nos. 3,073,262 and 3,070,045. Still another machine for spinning substances is disclosed in commonly owned, co-pending U.S. Patent Application Serial No. 07/954,257 to Fuisz. The application discloses a spinner head including a heating element which defines a narrow, elongate opening providing a substantially non-tortuous path through which feedstock material subjected to flash-flow is projected. Various other spinning machines of the prior art are referenced therein. A basic spinning machine includes a spinning head with a heating element arranged circumferentially therearound. Sugar is introduced to the spinner head and dispersed along the heating element. Heat from the heating element thereby changes the physical structure of the sugar sufficiently to permit the sugar to flow through openings and form the floss product. In early models, heat is applied as the spinner head rotates whereby the floss product is generated. The early models had virtually no means for controlling the various factors that strongly influenced the quality of the spun product. These factors include: the temperature of the heating element and therefore the amount of power directed to the heating element, the size of the opening through which feedstock material is projected, and feed rate at which the feedstock material is fed into a feeder assembly for processing by the spinner head. In the more recent models, methods of controlling the several above-mentioned factors have been implemented. For example, commonly owned, co-pending U.S. Patent Application Serial No. 08/049,773 discloses a temperature feedback control method and apparatus to precisely control heating of the feedstock material during the flash flow process. Such temperature control ensures more consistent spin processing operation and a higher quality spun product. A method for attempting to control the volume of processing material within a spinner head or a melt spin machine is disclosed in U.S. Patent No. 3,930,043. The rate that sugar is fed to the spinner head is mechanically controlled by detecting a physical displacement of a portion of the sugar present within the head and shaped according to a vortex formed by the spinning head. More or less sugar is fed into the rotating head according to the detected physical displacement of the sugar therein. This method of feed rate control, however, is inexact. Shifts in the melt spin machine may shift the detectable mass rendering inaccurate displacement detection. Accordingly, the mass of sugar (or feedstock material) present in the spinner head may exceed or fall short of an amount commensurate with the spinning machine's ability to smoothly process it. Carbonization of the heating element and product burning are the likely result. It is therefore an object of this invention to provide a material processing method and apparatus for flash flow melt spin processing with feed rate control characteristics capable of preventing overloading of the processing head with an excessive volume of processing material. A still further object of the invention is to provide a material processing apparatus for flash flow melt spin processing having feed rate control achieved using a detected weight of the processing head to determine the flow rate of feedstock material into the processing head necessary for producing a high quality product. SUMMARY OF THE INVENTION In accordance with these and other objects of the invention, a material processing apparatus for flash flow melt spin processing is provided with feed rate control characteristics as defined in claim 1. The material processing apparatus also includes a load detector for supporting the spinner head assembly and detecting a force exerted by the spinner head assembly on the support means. A feed rate controller electrically connected to the a load detector determines a load of the material in the spinner head, comparing the load to a preselected load and determining a difference therefrom. A feeder assembly responsive to the difference causes the material to be supplied to the spinner head. The load is determined by one or more sensors which continuously weigh the spinner head assembly and detect the additional weight present there due to the load of feedstock material introduced to the head. A method of the present invention for flash-flow processing having feed rate control includes the steps of continuously detecting a load of feedstock material present within a spinner head and generating a load signal corresponding thereto, and comparing the load signal to a signal representative of a preselected load of the material. The method also includes the step of controlling the rate that the feedstock material is supplied to the spinner head according to the comparison signal. Preferably, the weight of feedstock material is continuously detected generating a weight signal which is then compared to a set point indicative of a preselected weight. The rate at which feedstock material is supplied to the head is thereby controlled. The present invention includes a feed rate controller for controlling a feed rate of feedstock material provided to a spinner head for flash flow processing. The feed rate controller includes at least one load detector positioned to support the spinner head for generating at least one load signal indicative of a load of feedstock material present in the spinner head. A process controller responsive to the load signal continuously compares the detected load to a preselected load, determining a difference between the detected and preselected loads. Control means responsive to such difference controls the feed rate. The process controller can include means for generating a select signal indicative of the preselected load and means for generating a process control signal according to a difference between the preselected load and the actual load, defined by at least one load signal; the control means are responsive to the process control signal. A summer may sum the load signal(s) and generate a summation load signal therefrom for use by the process controller for generating the process control signal. Preferably, a signal processor filters short term variations from the summation load signal. As a result of the process and apparatus of the present invention, the rate at which feedstock is provided to a spinner head for flash flow melt spinning may be controlled to prevent overloading and underloading of the spinner head with feedstock material. The controlled feed rate enables a consistently higher quality flash flow product to be produced resulting from the present invention's ability to provide a flow rate that is ideal for a selected feedstock. Further, the controlled flow rate of feedstock to the spinner head avoids carbonization of the heating element and product burning, common in flash flow processing machines of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a material processing apparatus including a feed rate controller of the present invention. FIG. 2 is a schematic block diagram depicting the feed rate controller of the present invention. FIG. 3 is a perspective view of an assembly for processing feedstock materials; FIG. 4 is a perspective view of an embodiment of a screw type feeder used with the present invention; and FIG. 5 is a perspective view of a spinner head in accordance with the present invention. DETAILED DESCRIPTION OF THE INVENTION A material processing method and apparatus is provided for flash flow melt spin processing having feed rate control characteristics. "Feedstock" as used herein refers to solid materials which flow when heated. The feedstock material undergoes intraparticle flow when heated prior to undergoing substantial degradation or decomposition. Feedstock materials useful herein include thermoplastic polymers as well as materials such as sugars, saccharides, polysaccharides, etc., which exhibit intraparticle flow when heated. Examples of such materials are sugars as disclosed in U.S. Patent No. 4,855,326, issued August 8, 1989, polydextroses as disclosed in U.S. Application Serial No. 881,603, filed May 12, 1992, maltodextrins (including corn syrup solids) as disclosed in U.S. Application Serial No. 847,595, filed March 5, 1992, and thermoplastic polymers such as disclosed in U.S. Application Serial No. PCT/US92/04053, filed May 13, 1992, and biodegradable polymers as disclosed in U.S. Application Serial No. 893,238, filed June 3, 1992, all of which are incorporated herein by reference. "Melt spinning" as used herein refers to a process by which feedstock material is subjected to flash flow sufficiently to deform and pass through an opening under a centrifugal force provided by a spinner head. After the flowable material is thrown through the opening at high speed, it instantaneously reforms as a solid having altered physical and/or chemical structure. The altered structure results from the forces acting on the material as it exits the head and is hurled outwardly during the brief period during which it experiences flash flow. In order to provide uniform high quality melt spun product, the present invention provides for controlling a feed rate of the load of feedstock material supplied to a spinner head of a melt spin machine during processing. In one embodiment, a feed rate controller of the present invention controls the feed rate of feedstock material to the spinner head according to a detected weight of feedstock material present in the spinner head. Figure 1 shows a spin processing apparatus 10 provided with a feed rate controller 12 of the present invention. The apparatus 10 includes a base 14 upon which is mounted a basin assembly 16. The feedstock material is provided from a hopper 18 through a feeder assembly 20 and out a chute 22. A funnel 24 directs feedstock material from the chute into basin assembly 16 to a spinner head 26 contained therein. The feeder assembly 20 is driven by feeder drive motor 28 to convey the feedstock material through chute 22 into spinner head 26. A motor shaft 30 mechanically connects spinner head 26 to spinner motor 32. The spinner head is caused to rotate at a selected speed about the axis of motor shaft 30, whereby the feedstock material is propelled directly against a heating element 34 (Figure 5). The materials are subjected to sufficient heat thereat to compel them to undergo flash-flow. Upon undergoing flash-flow, the materials are projected from the spinner head 26 into the basin assembly 16 due to the considerable centrifugal force generated by the spinner head's rotation. The morphology of the finished product, which reforms as a solid upon exiting the spinner head 26, depends upon the speed at which the spinner head is rotated, the temperature maintained by the heating element 34, the openings through which the material is projected, and the amount of feedstock material present in the spinner head during processing. Spinner motor 32, shaft 30 and spinner head 26 are supported by a number of motor mount members 36 mechanically connecting motor 32 to base 14. A first end of each motor mount 36 is attached at a top portion of motor 32. A second end of each motor mount member 36 is mechanically connected to a bottom portion of each of a plurality of load cells 40. A top portion of each of the plurality of load cells is connected to a top portion 38 of base 14. In such a manner, the spinner motor 32 and spinner head 26 are supported at load cells 40 via motor mount member 36. Load cells 40 detect the force required to support the above mentioned combination, i.e., its weight. Using the weight of the above mentioned assembly devoid of feedstock material as a normalized zero baseline, continual determination of the exact weight of feedstock material present within the spinner head 26 is determined during processing. The weight of a particular feedstock material can easily be correlated with a correct volume of the material. Desired volume of a particular feedstock material in the spinner head 26 may be preselected. Each load cell 40 generates a load signal proportional to the weight it detects. The preferred embodiment includes four (4) load cells. Each load cell is electrically connected via electrical wires 42 to feed rate controller 12. Feed rate controller 12 receives the load signals generated within each load cell 40 and determines therefrom the exact weight of processing material present within the spinner head 26. The feed rate controller 12 compares the determined weight to the preselected weight (or load) of the material being processed. Based on the comparison, the feed rate controller determines and adjusts a rate of flow of material to the spinner head. Figure 2 shows a block diagram of the preferred feed rate controller 12 depicted in Figure 1. Each load cell 40 is shown electrically connected to a summer section 44 via electrical wires 42. Summer section 44 electrically combines the load signals from each of the load cells 40 into one summation load signal. The summation load signal is transferred to a signal processor 46, where short term variations in the summation load signal due to such effects as mechanical vibration and wobble, inherent in the rotating system, are filtered out. The filtered summation load signal is transmitted from signal processor 46 to a process controller 48. Process controller 48 receives the filtered summation load signal, using it to generate a process control signal to control a motor speed controller 50. Motor speed controller 50 receives the process control signal and generates a feed rate control signal. The motor speed controller 50 provides the feed rate control signal to feeder drive motor 28. Feeder drive motor 28 is mechanically connected to feeder assembly 20 to control the rate of feeding material flowing to spinner head 26. In the preferred embodiment, process controller 48 is a microcomputer. The microcomputer within process controller 48 uses an algorithm implemented by computer code to derive the actual weight of the feedstock material within the spinner head 26. The process controller correlates a feedstock being processed to a preselected weight in the form of a set point or select signal for the particular feedstock material. The process controller compares the detected weight to the preselected weight, i.e., compares a signal indicative of the detected weight to the select signal. The preselected weight may be determined within the process controller 48 according to many factors related to a particular feedstock such as: desired end product morphology, processing temperature, ambient humidity, etc. The process controller 48 generates the process control signal based on the comparison of the detected and preselected weight thereby controlling the flow rate of material to the spinner head. If the weight sensed by load cells 40 is too small, i.e., the spinner head 26 does not contain the preselected load for a particular material being processed, the process controller 48 can change the magnitude of the process control signal provided to motor speed controller 50. The rate of the material flow to the spinner head 26 is increased thereby. If the weight sensed by load cells 40 is large, i.e., the spinner head 26 contains a load too large for a particular material being processed, the magnitude of the process control signal is again changed accordingly. The rate of material flow to the spinner head 26 is decreased thereby. The present invention is directed to controlling the rate at which feedstock material is delivered to a spinner head for flash flow processing. The preferred form of the invention detects the weight of feedstock material present in the spinner head, compares it to an ideal weight and adjusts the feed rate to the spinner head accordingly. The invention, however, is not limited to controlling the feed rate of feedstock material to the spinner head during processing based on weight detection. An operator interface 52 may supply processing information to process controller 48 in addition to information supplied by signal processor 46. The operator interface 52 provides information such as the amount of material required for optimal operation of spinner head 26 as well as various control parameters which may alter the result of the processing algorithm implemented by process controller 48. The operator interface 52 also may receive data from process controller 48 to inform an operator of the status of spin processing operation. The operator interface 52 can also enable an operator to void all calculation and select the desired load to be controlled, i.e., direct user control of the feed rate. Operator interface 52 bay take on any form, such as a keyboard 54, known to those skilled in the art. Fig. 3 shows a melt spin processing assembly 60 in which feedstock materials are fed to a spinner head 26 (Figure 1) where they may be subjected to a flash-flow process and collected in a basin or basket or air conveyed to another location or to a collection container. The assembly 60 includes hopper 18, chute 22, basin assembly 16 (which houses the spinner head), funnel 24 for directing material from the chute 22 to the spinner head 26, and base 14. Feeder assembly 20 is positioned at the base of the hopper 18, the chute 22 extending therefrom. The feeder assembly 20 is connected to a feeder drive motor 28 (Fig. 1) and may include any means known to those skilled in the art for moving material from the hopper 18 to the funnel 24 and into the spinner head 26. The base includes spinner motor 32 (Fig 1) for driving the spinner head 26. The spinner head may be driven in a known manner as described in U.S. Patent No. 4,872,821 (incorporated by reference herein), which has been converted to a variable speed drive system. Figure 4 shows an embodiment of the present invention utilizing a screw-type feeder for moving material from the hopper 18 into the spinner head 26. Screw-type feeder 62 is used in place of chute 22. Screw rotators 64 within the screw-type feeder are aligned with a feed axis 66. The screw rotators 64 are rotationally driven by feeder drive motor 28 (contained within feeder assembly 20) thereby causing feedstock to move from the hopper 18 into the funnel 24. Figure 5 show one embodiment of a spinner head 26 which may be used in accordance with a feed rate controller 12 (Fig. 1) of the invention. The spinner head includes a base member 84, a bottom insulating ring 66, a top insulating ring 68, an aluminum cap 70, and heating element 34. The base and cap may be made from stainless steel or other suitable material, while the insulating rings are preferably from a ceramic material or heat resistant polymer. The cap includes a cap opening 72 aligned with the funnel 24. Figure 5 shows a stem 74 which extends from the base 14. The stem includes slip rings 76, 78 which are engaged by brushes (not shown), and upright motor shaft 30 which is driven by motor 32 within the base 14. The stem 74 is similar to that disclosed in U.S. Patent No. 4,872,821, and functions in a similar manner. An electronic interface assembly is mounted to the base member 84, and powers the heating element 34. The present invention may utilize any type heating element known to those skilled in the art. The heating element 34 of the present embodiment is comprised of a cable 82 which is wound helically about the axis of rotation of the spinner head 26. While the cable 82 forms a single helix as shown in the drawing, it may alternatively be wound as a double helix or multiple helixes, i.e., such as eight separate cables. Cable heaters are well-known commodities, and are used in a number of applications, including some of the cotton candy machines discussed above. A suitable cable includes a core heating element (not shown) such as a nichrome, ALUMEL™ or INCONEL™ wire. INCONEL™ is a trademark for a nickel-chromium-iron alloy which is sold under the INCONEL™ mark. The outside sheath is also made of a corrosive-resistant alloy such as INCONEL™, and high temperature electrical insulation such as magnesium oxide. The spinner head 26 may also be provided with a continuous wall heating element with openings, such as slots, for permitting flash flow through the wall. The specific embodiments of the feed rate controller and apparatus for flash flow processing having feed rate control that are identified in the disclosure may be replaced by other means without materially affecting the feed rate control operation according to the invention. The invention accordingly is not limited to the precise embodiments disclosed, and various other changes and modifications may be affected therein by one skilled in the art without departing from the scope or spirit of the invention as defined by the claims.

Claims: An apparatus (10) for melt spin processing comprising: a spinner head assembly, which assembly includes a spinner head (26) having a continuous perimeter for spinning material Using heat and centrifugal force and spinner drive motors (32) connected to the head (26) for supplying centrifugal force thereto characterised in that the apparatus includes feed rate control means comprising at least one load detector (40) positioned to support the spinner head (26) and generate a load signal, which signal indicates a detected load of feedstock within the spinner head (26); a process controller (48) responsive to said load signal, the process controller (48) continuously comparing the determined load to a preselected load, determining a difference between the detected and preselected loads; and control means (50) responsive to said difference for controlling the rate at which feedstock is fed to the spinner head assembly. An apparatus as defined by claim 1, further comprising a signal processor for filtering short term variations from each said at least one load signal. An apparatus as defined by claim 1, characterised in that said process controller (48) includes means for receiving direct user input for controlling said feed rate. An apparatus as defined by claim 1, characterised in that said process controller (48) includes a microcomputer for determining said difference. An apparatus as defined by claim 1, characterised in that said process controller (48) includes means for generating a select signal indicative of the preselected load and means for generating a process control signal according to a difference between said select and said at least one load signals, and characterised in that said control means (50) includes means responsive to said process control signal. An apparatus as defined by claim 5, further comprising a summer (44) for receiving and summing each load signal and generating a summation load signal therefrom, and wherein said process controller (48) generates said process control signal according a difference between said select and said summation load signals. An apparatus as defined by claim 6, further comprising a signal processor (46) for filtering short term variations from said summation load signal. A method of melt spin processing characterised in that the method comprises the following steps: continuously detecting a load of feedstock in a spinner head and generating a load signal therefrom; comparing said load signal to signal for a preselected load and generating a comparison signal; controlling the rate at which feedstock material is supplied to the spinner head (26) in response to said comparison signal. A method as defined in claim 8, further comprising the step of filtering said load signal to remove short term variations therefrom. A method as defined by claim 8, characterised in that the step of continuously detecting includes detecting a weight of the feedstock material, and characterised in that said step of comparing includes comparing the detected weight with a preselected processing weight. A method as defined by claim 8, further comprising the step of inputting data for directly controlling said feed rate. An apparatus as defined by claim 1 comprising: a heating element (34) substantially continuous with the spinner head perimeter for generating said heat,; a feed rate controller(12) electrically connected to the load detection means (40) which uses said detected force to determine a load of the material being processed in the spinner head (26), comparing said load to a preselected load and determining a difference therefrom; and a feeder assembly (20) responsive to said difference that supplies the material. An apparatus as defined by claim 12, characterised in that said support means includes at least one load cell for generating at least one load signal indicative of said force, characterised in that said feed rate controller includes means to compare said at least one load signal to a select signal indicative of the preselected load and generates a feed rate control signal according thereto, and characterised in that said feeder assembly is responsive to said feed rate control signal. An apparatus as defined by claim 13, characterised in that said feed rate controller includes: a summer electrically connected to each said load cell for generating a summation load signal; a process controller electrically connected to said summer for comparing said summation load signal to said select signal and generating a process control signal from the comparison; and control means responsive to said process control signal for generating said feed rate control signal. An apparatus as defined by claim 14, characterised in that said feed rate controller includes a filter electrically connected to said summer for filtering short term variations from said at least one load signal. A method as defined by claim 8, characterised in that the step of controlling includes receiving direct user input. A method as defined by claim 16, characterised in that said step of continuously detecting includes detecting a weight of said feedstock material, and characterised in that said step of comparing includes comparing said detected weight to a preselected weight.

Inventors: BOGUE BEUFORD A, HRUBEC JOHN A, BOGUE, BEUFORD A., HRUBEC, JOHN A.
Applicants: FUISZ TECHNOLOGIES LTD, FUISZ TECHNOLOGIES LTD.
Application year: 1994
Main classification: A23G3
IPC codes: A23G3, D01D5